When I bought my plane, which has an SD-8 alternator as the primary power source, it came with an inline fuse on one of the two leads from the alternator.

The guy who installed it said it was an 8 amp alternator so he added a 10 amp inline fuse. But, I believe it provides 8 amps at 14 volts after regulation and the voltage where the fuse is installed is something like 20-25 volts AC. So, the max current there would probably be a bit less than 8 amps anyway, right?

Regardless, it has never blown, but I am wondering if it is even serving a useful purpose other than to increase the number of electrical connections in my plane?

The SD-8, under some conditions, is capable of 10A
of output. A fuse should be sized for at least 1.5
times the expected continuous load . . . 2x or
3x is not unreasonable giving the very fast action
of a fuse versus circuit breaker.

If the SD-8 feeder is 14AWG or larger, a 20A
fuse is the better choice . . . 30A would not
be out of line.

Hit the 'send' button too soon. The short
answer to your question: That feeder should
be protected. If you've not experienced a
nuisance trip of the 10A fuse, then there's
no pressing need to fiddle with it. If you
DO experience a nuisance trip in the future,
and upsize is indicated, I'd go for 20A

Bob . . .

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